Small, digital cameras integrated into mobile electronics such as mobile phones, personal digital assistants (“PDAs”) and music players are becoming ubiquitous. Each year, mobile phone manufacturers add more imaging features to their handsets, causing these mobile imaging devices to converge towards feature sets that consumers expect from stand-alone digital still cameras. At the same time, the size of these handsets is shrinking, making it necessary to accordingly reduce the total size of the camera modules while still adding imaging features. Optical zoom is a primary feature that many digital still cameras have that many mobile phones may not have, primarily due to the severe size constraints in mobile imaging devices.
Cameras (including digital cameras) may be arranged to receive electromagnetic radiation (such as visible light) through an aperture that can be defined by the camera based on a number of well known techniques. For example, an optical sub-system, including one or more lenses and/or other optical elements, may define the aperture such that the received radiation is imaged by the optical sub-system and a resulting image is directed towards a sensor region such as a sensor array that includes a plurality of detectors defining a sensing surface. The sensor region may be configured to receive the image and to generate a set of image data based on the image. In some common applications, such as when using conventional digital cameras to capture images, the camera may be aligned to receive electromagnetic radiation associated with scenery having a given set of one or more objects. In these applications the set of image data is, for example, represented as digital image data using an electrical signal conveyed by electrical conductors or stored using memory or other digital storage techniques. In addition, the set of image data can be processed using a number of known image processing techniques.
In the context of the present disclosure, “zoom” may be understood as a capability to provide different magnifications of the same scene and/or object by changing the focal length of an optical system, with a higher “level of zoom” being associated herein with greater magnification and a lower level of zoom being associated with lower magnification. In typical film-based cameras, as well as in conventional digital cameras, optical zoom can be accomplished with multiple lens groups that are moved along an optical axis of an imaging system for defining a range of different lens configurations. For any given configuration, the position of the lens groups determines a focal length specific to that configuration. Based on well known techniques, camera users can adjustably control the positioning of the lens groups for selecting a specific level of zoom. At any specific level of zoom associated with a selected focal length of a camera's optical sub-assembly, an image represents a portion of a given scene based in part on the field of view defined by the lens system. For example, an image plane can be defined by the camera's sensor region (such as a sensor array), and the resulting image represents a field of view consistent with (i) a shape and transverse extent of the sensor region's sensing surface, and (ii) the selected focal length. For a given camera, there is a tradeoff between zoom and field of view such that camera settings exhibiting longer focal lengths generally tend to result in a greater level of zoom in conjunction with correspondingly narrower field of view. Conversely, camera settings exhibiting comparatively shorter focal lengths tend to result in a lower level of zoom in conjunction with a wider field of view.
Certain film-based cameras and digital cameras utilize a fixed focus imaging system, and these cameras generally do not feature adjustable optical zoom. Fixed focus imaging systems are especially common in PDAs. The high complexity, cost and decreased durability typically associated with moveable lenses (e.g., in cameras having optical zoom) limit their use in inexpensive camera modules such as mobile phone camera modules and other low cost modules. Film based cameras with fixed focus imaging systems generally offer no means for the user to adjust the degree of magnification while preparing to take a picture. On the other hand, digital cameras having fixed optical focus can incorporate digital zoom to allow the user to control the level of zoom before and/or after capturing the image by generating a corresponding set of image data. For example, digital zoom can utilize computer-processed cropping followed by signal upsampling and data interpolation of the cropped image to convert the cropped image to the original display size. As a result, however, the resolution of the cropped, final image is decreased and the image quality suffers.